Rod antennas or horn antennas are generally used for microwave-based level measurement systems for products in containers or storage tanks, which can also be used measure interfaces between different dielectric materials. Rod antennas have a narrow and elongated configuration which are suitable for storage tanks having a small opening or flange size and a sufficient height for accommodating the antenna. Horn antennas are wider and shorter as compared to rod antennas. Advantages of horn antennas include moderate directivity (gain), a low standing wave ratio (SWR), broad bandwidth, and simple construction and adjustment.
Horn antennas are usually the antenna of choice for high pressure radar gauging. In the case of a small tank opening (<4 inch or 10.2 cm), horn antennas with such small diameters lack the gain and half-power beam width (HPBW) to generally meet required system accuracy. Hollow dielectric rod antenna are also known for high pressure radar gauging.